IP/Bras Profile

Your IP profile is closely related to the bRAS profile and is an indication of the maximum throughput speed your line can attain whilst that particular profile is in place.

According to BTw, the first Data Rate should be set within 75 mins of going live on maxDSL.
Most customers will find that their line has a profile set at the bRAS within 3 days, although it can take up to 10 days for some lines to fully stabilise.

The IP / bRAS profile is based on your lowest sync speed, and jumps up in 0.5Mb or 0.25 Mb stages.
So although you may get higher sync speed, your bRAS profile will limit you to what throughput speed you are likely to achieve.

~ How can I find out what my IP Profile is?

You can find out what your IP profile is currently set at by performing a Broadband Performance Test.

IP profile result

In addition your ISP should also be able to find out this information from data provided to them from BT called an Actuate Report.  Be aware though that not all ISP Help desks will know what this is, and it isn't always information that CS support staff - particularly on some of the larger ISPs - are able to see. bras profile


~ How often does it change?

Previously your IP profile would be amended within 75 mins for a decrease in sync speed, or after 3 days for an increase in sync speed.
Obviously this arrangement wasn't always the best solution since it could take several days to recover from one bad sync period such as during a thunderstorm.

With effect from Aug 2007, BT will introduce "Adaptive Max Logic" which will replace both the 3 day system and Blip logic. This should be of benefit to those who have suffered from an unusually low sync, although smaller increases will take a bit longer.

Your IP profile will continually change whilst you are on a maxdsl service dependant upon the speed at which you connect to the exchange at. Good Lines will seldom see any changes, but long lines are subject to frequent changes depending upon the connection speed.
Because of the way SNR behaves, most lines will achieve a better sync speed during the early part of the day than in the evenings.

~ What is "Adaptive Max Logic"?

  • Decreases in sync speed will still reflect in the IP profile within 75 mins.
  • Increases in sync speed will depend on the percentage of the increase and will vary between a few hours and up to 5 days.

A large % increase in sync speed should see the IP profile rise within 4-6 hours, whilst a small increase may take up to 5 days before the IP profile reflects the change. BT estimates that under "Adaptive Max Logic" more than 60% of increases will now occur before they would on the old 3 day system.

Examples:-

1. - Large increase - Line dropped to a 576 sync during a thunderstorm (profile = 500), after a resync it went back up to 7616 (profile 6500). Profile increase = 6000/500 *100 = 1200% increase which should occur in 4-6 hours.
2. - Small increase - Sync increase from 7616 (profile 6500) to 8128 (profile 7150) after interleaving removed. Profile increase = 650/6500*100 = 10% which may not take effect for 5 days.

How long it exactly takes for increases to be applied would also seem to depend on how busy the system is.

~ How is my IP Profile calculated?

It is based on your lowest sync speed over a period of time, and makes an allowance for TCP/ATM overheads. BT uses a range of figures based on the figure which you sync to the exchange at.

~ Why do we need an IP / bRAS profile?

The simple answer is to stop traffic "bottle-necking" at the exchange VPs. A maximum throughput level is needed to stop more data than your line can physically achieve being sent down the backhaul and being dropped at the DSLAM.

When we request data this will firstly comes down over high speed UK backbone (Colossus) to the RAS.
From the RAS traffic will traverse the ATM backhaul where it branches off to the different exchanges. These Virtual Paths on some exchanges can be relatively small (say 20-50 MB). If you have a lot of users at the same exchange requesting data coming off the backbone fast, this could soon swamp the VPs. Therefore BTs solution is to throttle the speed of "our" data at the RAS and not allowing data to travel down the VP at a speed any faster than our connection can handle.

The IP profile is a "net" figure after an allowance has been made for any processing overheads such as TCP/IP and ATM overheads.


~ Full list of available IP & bRAS profiles used by BT Wholesale on IPStream maxdsl products.

Sync speed (incr 32kb stages) IP profile bRAS ATM bit rate profile Maximum Throughput speed
(AAL5 Payload)
From To
     
160 kbps 256 kbps 135138Up to 135 kbps
288 kbps 384 kbps 250256Up to 0.25 Mbps
416 kbps544 kbps350370Up to 0.35 Mbps
576 kbps 832 kbps 500512Up to 0.5 Mbps
864 kbps 1120 kbps 750768Up to 0.75 Mbps
1152 kbps 1408 kbps 10001024Up to 1 Mbps
1440 kbps1696 kbps 12501280Up to1.25 Mbps
1728 kbps1984 kbps 15001536Up to 1.5 Mbps
2016 kbps2240 kbps 17501792Up to 1.75 Mbps
2272 kbps2816 kbps 20002048Up to 2 Mbps
2848 kbps3392 kbps25002560Up to 2.5 Mbps
3424 kbps3968 kbps30003072Up to 3 Mbps
4000 kbps4512 kbps35003584Up to 3.5 Mbps
4544 kbps5088 kbps40004096Up to 4 Mbps
5120 kbps5664 kbps45004608Up to 4.5 Mbps
5696 kbps6208 kbps50005120Up to 5 Mbps
6240 kbps6784 kbps55005632Up to 5.5 Mbps
6816 kbps7360 kbps60006144Up to 6 Mbps
7392 kbps7936 kbps65006656Up to 6.5 Mbps
7968 kbps8096 kbps70007168Up to 7 Mbps
8128 kbps 71507320Up to 7.15 Mbps

~ "Stuck bRAS profile"

Although not quite so common these days as when dslMAX was first introduced, there is still the odd occasion when a line seems to get what is known as a stuck bRAS profile.

When your line is first profiled the theory is that the DLM system should set your IP profile in line with your sync speed within the first 75 mins. If a profile is not correctly set then the default value of 2048/2000 is used. This may clear within 3 days and it may help if you say leave your router switched off overnight... but some lines just seem to get "stuck".

From my own observations this mostly appears to happen on the better quality lines - ie ones that don't loose sync or need any automatic DLM configurations.

If you suspect a stuck bRAS on your line then you will have to contact your ISP asking them to get BTw to clear a stuck bRAS profile fault.

 

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